A patent document 1 discloses a known conventional power steering device as follows.
This power steering device includes a power transmission mechanism configured to transmit a torque of an electric motor to a rack bar while converting the torque into an axial moving force of the rack bar. The power steering device includes a housing liquid-tightly covering an outer periphery pf the rack bar and the power transmission mechanism. When water enters an interior of the housing, the power steering device determines that the power steering device is abnormal, based on detection of the entrance of water by a water sensor disposed in the housing.
However, the conventional power steering device is confronted with a problem where the power steering device is capable of detecting the entrance of water into the housing by the water sensor, but is incapable of performing sufficient abnormality determination, for example, when foreign matter such as sand or dust other than water enters the interior of the housing, because of incapability of detecting such foreign matter.